Parametric stereo and multichannel coding methods are known to be scalable and efficient in terms of listening quality, which makes them particularly attractive in low bitrate applications. In cases where the bitrate limitations are of a transitory nature (e.g., network jitter, load variations), however, the full benefit of the available network resources may be obtained through the use of an adaptive distribution format, wherein a relatively higher bitrate is used during normal conditions and a lower bitrate when the network functions poorly.
Existing adaptive distribution formats and the associated (de)coding techniques may be improved from the point of view of their bandwidth efficiency, computational efficiency, error resilience, algorithmic delay and further, in audiovisual media distribution, as to how noticeable a bitrate switching event is to a person enjoying the decoded media. The fact that legacy decoders can be expected to remain in use parallel to newer, dedicated equipment poses a limitation on such potential improvements insofar as backward compatibility must be maintained.
Dynamic range control (DRC) techniques for ensuring a more consistent dynamic range during playback of an audiovisual signal are well known in the art. For an overview, see T. Carroll and J. Riedmiller, “Audio for Digital Television”, published as chapter 5.18 of E. A. Williams et al. (eds.), NAB Engineering Handbook, 10th ed. (2007), Academic Press, and references cited therein. Such techniques may enable a receiver to adapt the dynamic range of an audiovisual signal to suit relatively unsophisticated playback equipment, while the signal itself is broadcast at full dynamic range, to the benefit of more refined equipment. A simple implementation of DRC may use a metadata field encoding a gain factor in the interval from 0 to 1, which the decoder may choose to apply or not.
Using known DRC techniques an encoded audiovisual signal may be transmitted together with metadata offering a user the capability of compressing or boosting the playback dynamic range to suit his or her preferences or manually adapting the dynamic range to the available playback equipment. However, known DRC techniques may not be compatible with adaptive bitrate coding methods, and switching between two bitrates may sometimes be accompanied by dynamic range inconsistencies, especially in legacy equipment. The present invention addresses this concern.
All the figures are schematic and generally only show parts which are necessary in order to elucidate the invention, whereas other parts may be omitted or merely suggested. Unless otherwise indicated, like reference numerals refer to like parts in different figures.